System and method for providing a wide aspect ratio flat panel display monitor independent white-balance adjustment and gamma correction capabilities

ABSTRACT

A system and method are described herein for controlling the white balance and providing gamma correction without compromising gray-scale dynamic range in a flat panel liquid crystal display (LCD). According to one embodiment of the present invention, the flat panel LCD includes electronic circuitry for coupling to a host computer to receive a white-balance adjustment control signal, and electronic circuitry for receiving image data to be rendered on the flat panel LCD. Further, the flat panel LCD of one embodiment is configured for coupling to a color-sensing device to receive optical characteristics data of the flat panel LCD detected by the color-sensing device. The white balance adjustment mechanisms include the provision of two or more light sources of differing color temperature, whose brightness can be independently varied (and distributed through a light distribution mechanism) to adjust color temperature without altering the grayscale resolution of the RGB colors. The present invention further includes white balance adjustment software and gamma correction software for generating white-balance adjustment control signals and appropriate gamma correction curves.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/120,960 filed Jul. 22, 1998 and entitled “System And MethodFor Providing A Wide Aspect Ratio Flat Panel Display Monitor IndependentWhite-Balance Adjustment And Gamma Correction Capabilities”, now U.S.Pat. No. 6,611,249, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/087,745, filed on May 29, 1998, now U.S. Pat.No. 6,366,270, and entitled “A Multiple Light Source Color BalancingSystem Within A Liquid Crystal Flat Panel Display,” by Evanicky andassigned to the assignee of the present invention.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention pertains to the field of display devices.More specifically, the present invention is related to the field ofgamma correction and white-balance adjustment in flat panel displays.

BACKGROUND OF THE INVENTION

[0003] Flat panel liquid crystal displays (LCDS) are popular displaydevices for conveying information generated by a computer system. Thedecreased weight and size of a flat panel display greatly increases itsversatility over a cathode ray tube (CRT) display. Flat panel LCDmonitors are used today in many applications including the computercomponent and computer periphery industries where flat panel LCDmonitors are an excellent display choice for lap-top computers and otherportable electronic devices. Because flat panel LCD technology isimproving, more and more flat panel LCD monitors are rapidly replacingCRT displays in other mainstream applications, such as desktopcomputers, high-end graphics computers, and as televisions and othermulti-media monitors.

[0004] In flat panel LCD monitors, much like conventional CRT displays,a white pixel is composed of a red, a green and a blue color point or“spot”. When each color point of the pixel is excited simultaneously andwith the appropriate energy, white can be perceived by the viewer at thepixel screen position. To produce different colors at the pixel, theintensity to which the red, green and blue points are driven is alteredin well known fashions. The separate red, green and blue data thatcorresponds to the color intensities of a particular pixel is called thepixel's color data. Color data is often called gray scale data. Thedegree to which different colors can be achieved within a pixel isreferred to as gray scale resolution. Gray scale resolution is directlyrelated to the amount of different intensities, or shades, to which eachred, green and blue point can be driven.

[0005] The method of altering the relative color intensities of thecolor points across a display screen is called white balance adjustment(also referred to as color balance adjustment, color temperatureadjustment, white adjustment, or color balancing). In a display, the“color temperature” of white correlates to the relative percentagecontributions of its red, green and blue intensity components. Inaddition, the “color temperature” of white correlates to the luminousenergy given off by an ideal black body radiating sphere at a particulartemperature expressed in degree Kelvin (K). Relatively high degree Kcolor temperatures represent “white” having a larger blue contribution(e.g., a “cooler” look). Relatively small degrees K color temperaturesrepresent “white” having a larger red contribution (e.g., a “warmer”look). Generally, the color temperature of a display screen is adjustedfrom blue to red while avoiding any yellow-ish or green-ish variationswithin the CIE chromaticity diagram.

[0006] In conventional CRT devices, white balance is adjusted byindependently altering the voltage gains of the primary electron guns(e.g., red, green and blue guns) depending on the desired colortemperature. However, this prior art color balancing technique reducesthe dynamic gray scale range of some or all of the RGB colors, as wellas the overall color gamut of the display. In some conventional flatpanel LCDs, a shift in color temperature may be achieved by adjustingthe relative intensities of the RGB gray levels in a manner analogous tothe adjusting of the gain of the electron guns of the CRT devices.However, this prior art method also causes the LCDs to lose dynamic grayscale range and color gamut.

[0007] Another prior art method of adjusting the white balance within aflat panel LCD screen pertains to altering the physical color filtersused to generate the red, green and blue color points. By altering thecolor of the filters, the color temperature of the LCD screen can beadjusted. However, this adjustment is not dynamic because the colorfilters need to be physically (e.g., manually) replaced each timeadjustment is required. It would be advantageous to provide a colorbalancing mechanism for a flat panel LCD screen that can respond,dynamically, to required changes in the color temperature of thedisplay.

[0008] The white balance adjustment for a display is important becausemany users want the ability to alter the display's color temperature fora variety of different reasons. For instance, the color temperaturemight be varied based on a viewer's personal taste. In other situations,color temperature adjustment may be needed to compensate formanufacturing variations in the display. In some situations, colortemperature adjustment can correct for the effects of aging in somedisplays. Particularly, color critical applications such as pre-presssoft proofing, desktop publishing, graphics design, medical imaging, anddigital photography and video editing, etc., require white balancevalues and gamma values of different displays to be precisely matched inorder to accurately view and exchange images with confidence. Thus,without an efficient and effective method of providing dynamic whitebalance adjustment capabilities, flat panel LCDs have heretofore beenunused in color critical applications which require precise colorcalibration and matching. Therefore, what is needed is an efficient andeffective method of providing dynamic white balance adjustmentcapabilities in flat panel LCDS.

[0009] Accordingly, the present invention provides a display formechanism and method for dynamically adjusting the color balance of aflat panel liquid crystal display without compromising the gray-scaleresolution of the pixels. Further, the present invention provides amechanism and method for adjusting the color balance of a flat paneldisplay screen without complicated circuitry. Embodiments of the presentsolution also performs gamma correction and frame rate time domainmodulation to reduce scalloping and visual artifacts. These and otheradvantages of the present invention not specifically mentioned abovewill become clear within discussions of the present invention presentedherein.

SUMMARY OF THE INVENTION

[0010] A system and method are described herein for controlling thewhite balance and providing gamma correction without compromisinggray-scale resolution in a flat panel liquid crystal display (LCD).According to one embodiment of the present invention, the flat panel LCDincludes electronic circuitry for coupling to a host computer to receivea white-balance adjustment control signal, and electronic circuitry forreceiving image data to be rendered on the flat panel LCD. Further, theflat panel LCD of one embodiment is configured for coupling to alight-sensing device to detect optical characteristics of the flat panelLCD.

[0011] According to one embodiment of the present invention, the flatpanel LCD comprises a large display area liquid crystal display screenhaving an aspect ratio that is greater than 1.3:1. In one embodiment,the aspect ratio is substantially 1.6:1, having 1,600 pixels across thehorizontal and 1,024 pixels along the vertical. In this embodiment, theflat panel LCD is an SXGA-wide aspect ratio flat panel display monitorhaving high-resolution for displaying high-information content. Thisembodiment is particularly well suited for displaying text, graphics andother types of still and/or motion audio/Visual works. The wide aspectratio allows the display of multiple pages, side-by-side, therebyfacilitating certain tasks such as desktop publishing, pre-presssoft-proofing, video and digital photography editing, medical imaging,and graphics animation and design. The flat panel display of the presentinvention further includes compensation film layers for providingenhanced off axis viewing capability in the horizontal and verticalaxes.

[0012] Significantly, the flat panel LCD of one embodiment of thepresent invention provides white-balance adjustment capabilities. Thewhite balance adjustment mechanisms include the provision of two pairsof light sources of differing color temperature, whose brightness can beindependently varied (and distributed through a light distributionmechanism) to adjust color temperature without altering the dynamicrange of the grayscale resolution of the RGB colors. The flat paneldisplay of the present invention also provides a white-balanceadjustment control input for receiving a white-balance adjustmentcontrol signal, and a control circuit responsive to the white-balanceadjustment control signal for adjusting color temperature of the displayby altering the brightness of the appropriate light sources. In oneembodiment of the present invention, a white balance adjustment controlsignal is generated by the host computer, and is transmitted to the flatpanel LCD unit via an inter-integrated circuit (12C) bus.

[0013] According to one embodiment of the present invention, the flatpanel LCD monitor is configured for coupling to a digital computersystem to receive image data to be rendered on the flat panel LCDmonitor, and to receive control signals such as white-balance adjustmentcontrol signals and power management control signals. In the presentembodiment, a dual-channel low voltage differential signal (LVDS)interface is used for transmitting image data from the host computer tothe flat panel LCD unit. This interface provides sufficient bandwidthfor displaying high information content image data. In one embodiment ofthe invention, the host computer includes a color look-up table forproviding gamma correction to the image data on the fly. One embodimentof the present invention further includes white balance adjustmentsoftware and gamma correction software for generating white-balanceadjustment control signals and appropriate gamma correction curves. Inone embodiment, the host computer further comprises frame-rate timedomain modulation circuitry for processing the image data in order toreduce scalloping effects and other visual artifacts.

[0014] According to one embodiment of the present invention,light-sensing device comprises a low-cost luminance sensor speciallydesigned for coupling to a flat panel LCD monitor during monitorcalibration. The specially designed luminance sensor is not configuredfor attaching to the flat panel display by suction. Rather, theluminance sensor is configured for attaching to the flat panel displayduring monitor calibration by non-suction attachment means. By usingnon-suction type attachment means, optical characteristics of the flatpanel LCD monitor are not distorted during monitor calibration.

[0015] Significantly, during monitor calibration, luminance values ofthe flat panel LCD monitor are measured by the luminance sensor. Theluminance values are then used to construct the optical characteristicsof the flat panel LCD monitor. The constructed optical characteristicsare then matched to a set of target, or reference, opticalcharacteristics. The host computer then adjusts the white balance of theflat panel LCD monitor and/or the gamma values of the RGB colorsaccording to any discrepancies between the constructed opticalcharacteristics and the reference optical characteristics until aprecise match is achieved. In this way, precise color calibration isachieved in flat panel LCD monitors with an inexpensive luminancesensor.

[0016] Embodiments include the above and wherein the large area wideaspect ratio liquid crystal flat panel display screen is non-emissiveand further comprises: a first light source of a first colortemperature; and a second light source of a second color temperaturedifferent from the first color temperature, the first and second lightsources positioned to illuminate the wide aspect ratio liquid crystalflat panel display screen with light having a net color temperature thatis dependent on an intensity of the first light source and an intensityof the second light source wherein the first and the second lightsources alter the net color temperature of the light, within apredetermined color temperature range, by controlling the intensity ofthe first light source and the intensity of the second light source.Additionally, the flat panel display screen may comprise a light pipeoptically coupled to receive light from the first light source and saidlight source for illuminating the liquid crystal flat panel displayscreen with the light from the first and second light sources.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and form apart of this specification, illustrate embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention.

[0018]FIG. 1 illustrates an exemplary computer system used as part of acomputer graphics system in accordance with one embodiment of thepresent invention.

[0019]FIG. 2 illustrates a display assembly of the present inventionincluding wide aspect ratio display, stand and base components.

[0020]FIG. 3 is a cross section through the layers of the wide aspectratio liquid crystal display according to one embodiment of the presentinvention.

[0021]FIG. 4 illustrates an extraction pattern disposed on the surfacearea of a light pipe in accordance with embodiments of the presentinvention that use a two light sources.

[0022]FIG. 5 illustrates a cross section of the lighting configurationof the LCD panel embodiment of FIG. 3 showing the orientation of theextraction patterns in accordance with the present invention.

[0023]FIG. 6 illustrates the CIE chromaticity diagram including theblack body curve and the daylight white locus.

[0024]FIG. 7 illustrates an exemplary driver circuitry for the flatpanel LCD monitor according to one embodiment of the present invention.

[0025]FIG. 8 illustrates an exemplary control logic for the monitor ofone embodiment of the present invention including the exemplary drivercircuitry of FIG. 7.

[0026]FIG. 9 illustrates an exemplary set up of the present system ofproviding independent white balance adjustment and, gamma correctioncapabilities to a flat panel LCD monitor as illustrated in FIG. 2.

[0027]FIG. 10 is a block diagram of graphics subsystem of FIG. 1 infurtherance of one embodiment of the present invention.

[0028]FIG. 11A illustrates uncorrected voltage response curve of atypical twisted nematic liquid crystal layer of a liquid crystal displayscreen according to one embodiment of the present invention.

[0029]FIG. 11B illustrates the “scalloping” effect in theluminosity-grayscale relationship caused by the “pinning” particularvoltages of the LCD source drivers.

[0030]FIG. 12 illustrates an exemplary LVDS implementation of thedigital video signal interface according to one embodiment of thepresent invention.

[0031]FIG. 13 illustrates driver circuitry for the wide aspect ratioflat panel display according to another embodiment of the presentinvention.

[0032]FIG. 14A illustrates a side view of one embodiment of an LCD-safelight sensing device for measuring the optical characteristics of theflat panel LCD monitor according to the present invention.

[0033]FIG. 14B illustrates a front view of one embodiment of an LCD-safelight sensing device for measuring the optical characteristics of theflat panel LCD monitor according to the present invention.

[0034]FIG. 14C illustrates a hanger for mounting light sensing device800 to flat panel LCD screen according to one embodiment of the presentinvention.

[0035]FIG. 14D illustrates a luminance sensor mounted to flat panelmonitor using hanger according to the present embodiment.

[0036]FIG. 15 is a flow diagram illustrating the processing of profilinga flat panel LCD monitor according to one embodiment of the presentinvention.

[0037]FIG. 16 is a flow diagram illustrating the process of calibratinga flat panel LCD monitor according to one embodiment of the presentinvention.

[0038]FIG. 17 illustrates an exemplary graphics user interface (GUI) ofthe white balance adjustment and gamma correction software infurtherance of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0039] Reference will now be made in detail to the present embodimentsof the invention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepresent embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims. Furthermore, in the following description, forpurposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be obvious, however, to one skilled in the art, upon reading thisdisclosure, that the present invention may be practiced without thesespecific details. In other instances, well-known structures and devicesare not described in detail in order to avoid obscuring aspects of thepresent invention.

[0040] Unless specifically stated otherwise as apparent from thefollowing discussions, it is appreciated that throughout the presentinvention, discussions utilizing terms such as “receiving”,“determining”, “composing”, “storing”, or the like, refer to the actionsand processes of a computer system, or similar electronic computingdevice. The computer system or similar electronic device manipulates andtransforms data represented as physical (electronic) quantities withinthe computer system's registers and memories into other data similarlyrepresented as physical quantities within the computer system memoriesinto other data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission, or display devices.

Computer System Environment of the Present Invention

[0041] With reference to FIG. 1, portions of the present invention arecomprised of computer-readable and computer executable instructionswhich reside, for example, in computer-usable media of a computersystem. FIG. 1 illustrates an exemplary computer system 10 used as apart of a system for providing white balancing and gamma correction fora flat panel monitor in accordance with one embodiment of the presentinvention. It is appreciated that computer system 10 of FIG. 1 isexemplary only and that the present invention can operate within anumber of different computer systems including general purpose computersystems, embedded computer systems, and stand alone computer systemsspecially adapted for generating and displaying graphics images. It isalso appreciated that the various aspects of the present invention canbe made to function if the flat panel monitor is addressed by a remotecomputer system, or a “server,” which also interacts with other similarflat panel monitors within its network.

[0042] Computer system 10 of FIG. 1 includes an address/data bus 11 forcommunicating information, and a central processor unit 12 coupled tobus 11 for processing information and instructions. Computer system 10also includes data storage features such as computer-usable volatilememory 14, e.g. random access memory (RAM), coupled to bus 11 forstoring information and instructions for central processor unit 12,computer-usable non-volatile memory 13, e.g. read only memory (ROM),coupled to bus 11 for storing static information and instructions forthe central processor unit 12, and a data storage device 15 (e.g., amagnetic or optical disk and disk drive) coupled to bus 11 for storinginformation and instructions. Computer system 10 further includes aserial port 18 for coupling to peripheral devices such as a colorsensing device. A graphics subsystem 19, which may include a graphicsco-processor for offloading computational burden from central processorunit 12 and embedded DRAM for increased memory bandwidth, coupled to bus11, is also included in computer system 10 of FIG. 1. In one embodiment,graphics subsystem 19 is configured for coupling to a flat panel LCDmonitor for displaying information and image data. Details of thegraphics subsystem 19 and the interface to the flat panel LCD monitorwill be discussed in detail below.

[0043] Computer system 10 of the present invention also includes anoptional alphanumeric input device 16 including alphanumeric andfunction keys coupled to bus 11 for communicating information andcommand selections to central processor unit 12. Computer system 10 alsooptionally includes a cursor control device 17 coupled to bus 11 forcommunicating user input information and command selections to centralprocessor unit 12. Optional cursor control device 17 allows the computeruser to signal dynamically the two-dimensional movement of a visiblesymbol (cursor) on a display screen. Many implementations of cursorcontrol device 17 are known in the art including a trackball, mouse,touch pad, joystick, or special keys on alphanumeric input device 16capable of signaling movement of a given direction or manner ofdisplacement. Alternatively, it will be appreciated that a cursor can bedirected and/or activated via input from alphanumeric input device 16using special keys and key sequence commands. The present invention isalso well suited to directing a cursor by other means such as, forexample, voice commands. Computer system 10 may further include acommunication device (e.g. a modem) for communicating with a computernetwork.

Wide Aspect Flat Panel LCD Monitor of the Present Invention

[0044]FIG. 2 illustrates a monitor 216 in accordance with the presentinvention. The monitor 216 includes a display screen 210 for viewinghigh information content display. The flat panel display screen 210(“display 210”) of the present invention is digitally addressed in an(x, y) matrix of pixels over the entire area of the display. Displayscreen 210 includes a thin film transistor (TFT) liquid crystal displaylayer. The monitor 216 is coupled to a height adjustable stand 214 thatis supported by base 212. Stand 214 (or “tower”) allows both elevationand tilt adjustments. The monitor 216 of the present invention is alarge area wide aspect ratio flat panel monitor having high resolutionfor the display of high information content, such as graphics imagesand/or textual information including alphanumeric characters.

[0045] The monitor 216, in one implementation, is high resolutionsupporting the SXGA-Wide display format. The SXGA-Wide display formathas 1,600 pixels across the horizontal dimension and 1,024 pixels downthe vertical dimension. The aspect ratio of the SXGA-Wide compliantimplementation of the monitor of the present invention is approximately1.6:1. Within the context of the present invention, an aspect ratiogreater than 1.3:1 is considered to be a wide aspect ratio. The presentinvention having a display screen of 369.6 mm by 236.54 mm is thereforea large viewing area wide aspect ratio flat panel display unit. Becausethe pixel pitch (e.g., the distance between pixel centers) of themonitor 216 is 0.231 mm, it is very well suited for the display oftextual information (e.g., alphanumeric characters) as well as graphicimages, both being high information content. Therefore, the monitor 216of the present invention is well suited for desktop publishingapplications, graphics design applications, digital photography andvideo applications, medical imaging, prepress soft-proofing, etc. A moredetailed description of the wide aspect ratio flat panel LCD monitor 216can be found in copending U.S. patent application Ser. No. 09/120,983,filed Jul. 22, 1998, and entitled “A Large Area Wide Aspect Ratio FlatPanel Monitor Having High Resolution for High Information ContentDisplay,” which is hereby incorporated by reference.

[0046]FIG. 3 is a cross section of the layers of the flat panel displayscreen 210 in accordance with one embodiment of the present invention.The flat panel display 210 can be used with a fixed-in-placebacklighting unit or can be used with a removable backlighting assembly.Also, although FIG. 3 illustrates an edge lighting embodiment, display210 can also be directly backlit as described further below. The layersof display screen 210 are described from the bottom up ending with theviewed surface 210 a.

[0047] The flat panel display 210, in accordance with one embodiment ofthe present invention, provides white balance adjustment byindependently varying the brightness of two pairs of light sources(e.g., CCF tubes) 132 and 136 that belong to a lighting configuration160. For a predetermined range of color temperatures, having a minimumtemperature (e.g., 5,000 K) and a maximum temperature (e.g., 7,000 K), afirst pair of light sources 132 are provided that have a wavelengthspectrum with an overall color temperature less than the minimumtemperature of the predetermined range; herein, light sources 132, withthis characteristic are called the “red” light sources for convenience.Also, a second pair of light sources 136 are provided that has awavelength spectrum with an overall color temperature that is greaterthan the maximum temperature of the predetermined range; herein, lightsources 136 with this characteristic are called the “blue” light sourcesfor convenience.

[0048] Significantly, the present invention provides for a mechanism andmethod for adjusting the brightness of the two pairs of light sources132 and 136 of lighting configuration 160. Particularly, the monitor 216includes an white-balance adjustment control signal input configured forcoupling to a digital computer system to receive a white-balanceadjustment control signal, and control circuitry responsive to thewhite-balance adjustment control signal for controlling the brightnessof the two pairs of light sources 132 and 136. In addition, in oneembodiment of the present invention, the monitor 216 further comprisescircuitry configured for coupling to a light-sensing device (e.g. ancalorimeter or a luminance sensor) to measure optical characteristicsdata of the monitor 216. Furthermore, in that embodiment, the monitor216 may further comprise a color characteristics data output forproviding to the digital computer system the characteristics data to beused during calibration. The calibration process, as well as the digitalcomputer system, the mechanisms for gamma correction and white-balanceadjustment, and various embodiments of the light sensing device will bediscussed in detail below.

[0049] Also in the lighting configuration 160 shown in FIG. 3, the redlight sources 132 are optically coupled to provide light to a light pipe130. The red light sources 132 are positioned along an edge of the lightpipe 130. Likewise, the blue light sources 136 are optically coupled toprovide light to light pipe 130. The blue light sources 136 are alsopositioned along an edge of light pipe 130. In the embodiment 160 ofFIG. 3, the light sources 132 and 136 are long thin tubes which arepositioned on opposite sides of the planar light pipe 130. The lightsources 132 and 136 are positioned to be substantially parallel witheach other. The power supply for each pair of light source 132 and 136receive a separate voltage signal for independently controlling itsbrightness with respect to the other pair of light source. It isappreciated that the positions of the red tubes 132 and the blue tubes136 can be switched without departing from the scope of the invention.Other embodiments of the light configuration in accordance with thepresent invention, such as “L-shaped” light tubes, may be found inco-pending U.S. patent application Ser. No. 09/087,745, filed on May 29,1998, and entitled “A Multiple Light Source Color Balancing SystemWithin A Liquid Crystal Flat Panel Display,” now U.S. Pat. No. 6,366,270B1, and copending U.S. patent application Ser. No. 09/120,983, filedJul. 22, 1998 and entitled “A Large Area Wide Aspect Ratio Flat PanelMonitor Having High Resolution For High Information Content Display,”both of which are incorporated by reference.

[0050] Within display screen 210 of FIG. 3, a rear reflector layer 138is positioned on one side of the light pipes. On the other side of thelight pipes, diffuser layers 460 and 467 (mylar) are positioned next toone or more brightness enhancement layers (BEFs) 465. An air gap 455 isthen disposed. Layer 460 can optionally be covered by a protective layer(not shown). Layer 460 is then followed by a back or rear polarizerlayer 450 that is positioned next to the air gap 455. The display screen210 includes the back polarizer layer 450 followed by bi-refringentcompensation film 445 which is followed by a back glass layer 440.

[0051] The back glass layer 440 of FIG. 3 is followed by a selectivelyenergized transistor layer 435 and an LCD layer 430, followed byred/green/blue color filter layers 425. The TFT layer 435 is composed ofselectively addressed amorphous silicon thin film transistors (TFT)which charge up their respective capacitors. The color filter layer 425is followed by a front glass layer 420. The front glass layer 420 isfollowed by another compensation film layer 415 (e.g., a birefringencecompensation film layer) which is followed by a second or frontpolarizer layer 410. A protective coating layer 405 is placed in frontof the front polarizer layer 410 and provides a non-glare viewingsurface.

[0052] It is appreciated that the present invention's use ofcompensation film layers for improving view angle, in lieu of using dualdomain technology as done in the prior art, has several advantages.First of the advantages is a significantly reduced manufacturing processwhereby three major steps are used by the present invention rather than15 steps required of dual domain technology. Namely, the presentinvention utilizes a first step of applying polyimide, a second step ofbaking and a third step of rubbing. By reducing the process steps from15 to 3, thereby eliminating many of the steps required of dual domaintechniques, the use of compensation film layers by the present inventionsignificantly reduces manufacturing costs for monitor 216 whileimproving view angle both vertically and horizontally. It is appreciatedthat the present invention utilizes the compensation film layers 445 and415 to increase both horizontal and vertical viewing angles of themonitor 216. It is further appreciated that the present inventionutilizes the compensation film layers 445 and 415 to increase thehorizontal and vertical viewing angles of a large area monitor with awide aspect ratio for viewing high information content images and havingthe colors of those images be consistent over that wide area.

[0053] The liquid crystal layer 430 of FIG. 3, in one embodiment of thepresent invention, is characterized in that it is a twisted nematicliquid crystal layer. In a first alternative embodiment, the liquidcrystal layer 430 is an in-plane switching (IPS) layer without amolecular pre-tilt angle thereby increasing the off-axis viewingcapability of monitor 216. In a second alternative embodiment, theliquid crystal layer 430 is an antiferroelectric layer also used withouta molecular pre-tilt angle thereby increasing the off-axis viewingcapability of monitor 216. In these embodiments, although viewing anglesare increased, there are some limitations: response times of the IPSdisplay is somewhat affected due to the fact that IPS liquid crystalsare somewhat slower than twisted nematic liquid crystals; andanti-ferroelectric liquid crystals have difficulties in displaying largenumber of gray levels without special addressing circuitry.

[0054] The white balance or color temperature of display screen 210 ismaintained and adjusted using the two pairs of independently controlledlight sources 132 and 136. The white balance is adjusted by altering thebrightness of the pairs of light sources 132 and 136 independently. Thephosphor mix (e.g., contribution of red, green and blue phosphor) of thetwo pairs of light sources 132 and 136 is selected so that the whitebalance can be adjusted by varying the brightness of the light sources.The light pipe 130 is acrylic and contains an extraction system thatuniformly and independently distributes the light from each light sourceacross the viewing area of the display.

[0055] In one embodiment, the light sources 132 and 136 are cold cathodefluorescent (CCF) tubes and, in another embodiment, hot cathodefluorescent (HCF) tubes are used. Constraints are placed on the amountof brightness variation tolerated during white adjustment such that theoverall brightness of the display never decreases below a percentage ofthe maximum brightness output by the light sources 132 and 136. In oneimplementation, this percentage is selected at 70 percent which requiresthe ratios of the phosphors in the CCF tubes to be adjusted accordingly.

[0056]FIG. 4 illustrates a top view of an exemplary extraction pattern144 a that can be applied to the bottom of light pipe 130 within displayscreen 210. The extraction pattern 144 a is designed to uniformlyilluminate the LCD layer 430, at any brightness. Extraction dots areapplied directly to the lower surface of the light pipe 130. Toaccomplish this uniform distribution of light, extraction dots decreasein size in a proportion to their distance from the middle of the lightpipe 130. Extraction dots 150 a are smaller since they are relativelyclose to the light sources 132 and 136. Extraction dots 150 b areslightly larger since they are relatively farther from to the lightsources 132 and 136 than dots 150 a. It is appreciated that extractionpattern 144 a also includes larger sized dots 150 d at the corners nearthe light source 132 because the tube 132 is not as bright at the endsas in the middle sections of the tube. Variations in the extraction dotpatterns, which may be equally applied to the present invention, may befound in U.S. Pat. No. 5,593,221, by Evanicky, et al. which is herebyincorporated by reference.

[0057]FIG. 5 illustrates the lighting configuration 160 of light pipeand light sources (as shown for display 210 of FIG. 3) taking intoconsideration the orientation of its light extraction pattern. Withindisplay screen 210, extraction pattern 144 is designed to uniformlydistribute light to the LCD layer 430, as the brightness of lightsources 132 and 136 varies. Light extraction pattern 144 is shown inFIG. 5 in cross section as a thin line applied to the underside of lightpipe 130. As shown, the dot sizes decrease within pattern 144 from themiddle of the light pipe 130 towards the edges of the light pipe 130.

[0058]FIG. 6 illustrates a CIE chromaticity diagram 190. In oneembodiment of the present invention, when adjusting the intensities oflight sources 132 and 136, the resultant color temperature substantiallyholds to the black body curve 200 of diagram 190. FIG. 6 illustrates aCIE chromaticity diagram 190 illustrating chromaticity coordinates alongthe horizontal and vertical. Within the diagram 190, the green portion194 is toward the top with yellow 192 between green 194 and red 198.Blue 196 is toward the left. A black body curve 200 represents thechromaticity displayed by an ideal black body, typically approximated bya tungsten filament, heated to various degrees Kelvin. For instance,from point D to point A along curve 200, the curve represents the coloremitted from the tungsten filament from 6,500 degrees K to 2856 degreesK. As shown, the blackbody curve 200 traverses from blue 196 to the red198 without straying much into the yellow 192 or green 194 regions. Inan alternative embodiment of the present invention, when adjusting therelative intensities of the light sources 132 and 136, the resultantcolor temperature substantially holds a Daylight White Locus 199. TheDaylight White Locus 199, which is preferably used in the publishingindustry, is roughly parallel to the Black Body Curve 200. However, theDaylight White Locus 199 is of a greater energy that the Black BodyCurve 200, and, as illustrated in FIG. 6, has a larger green component.

[0059] The light sources 132 and 136 (FIG. 5) selected in accordancewith the preferred embodiment of the present invention are those thatilluminate with a color temperature that is near the Daylight WhiteLocus 199 when their brightness is adjusted within a predetermined colortemperature range (e.g., 5,000 to 7,000 K). That is, the color balancingsystem of the present invention allows adjustments to the colortemperature of the flat panel display screen 210 that remain close tothe Daylight White Locus 199.

[0060]FIG. 7 illustrates LCD control board circuitry 500 used fordriving the large screen wide aspect ratio, high resolution, displayscreen 210 of the present invention. Circuitry 500 is located withindisplay monitor 216 (FIG. 2). Circuitry 500 receives signals from aninformation originating source, e.g., computer system 10 (FIG. 1) asshown in the configuration of FIG. 7. The digital computer system 10generates display output signals (e.g., video output signals) which arecompliant with the low voltage differential voltage signals (LVDS) videoformat and in one implementation are 85 MHz. These display signals aresupplied over digital bus 515 to an LVDS receiver 520 which alsocontains timing converter circuitry. In order to provide sufficientbandwidth for rendering images on the wide aspect ratio monitor 216, inthe present embodiment, a dual channel LVDS interface is used wherevideo data is sent at the rate of two pixels for each LVDS output clock.The timing converter circuitry and the LVDS receiver 520 can beimplemented using application specific integrated circuitry (ASIC)technology. The dual channel LVDS interface will be discussed in greaterdetail below.

[0061] Although LVDS signal standard is employed in one embodiment ofthe present invention, other signal transmission standards can also beused by the present invention for the display signal including emittercoupled logic (ECL) and transition minimized differential signaling(TMDS) technologies. It should be apparent to those of ordinary skill inthe art, upon reading the present disclosure, that other signaltransmitting standards having sufficient bandwidth and suitable forsupporting a wide aspect ratio flat panel LCD screen may also be used.

[0062] An analog power supply 525 of FIG. 7 provides power signals todrivers 530 a-530 c for driving the flat panel display 210. Circuit 520supplies the drivers 530 a-530 c with timing and data signals compliantwith the LVDS signal format. The data signals include color data (RGB)for selectively updated rows of pixels of display screen 210. A pixel ondisplay screen 210 includes one red, one green and one blue sub-pixel.The pixels are organized around red, green and blue stripes and have auniform pixel pitch within display screen 210. In one embodiment, thepixel pitch is approximately 0.231 mm making display screen 210approximately 17.3 inches long along the diagonal direction for a highresolution of 1,600 pixels horizontally by 1,024 pixels vertically.

[0063] Display screen 210 includes a selectively energized transistorlayer 435 (FIG. 7) and each transistor corresponds to a color part of apixel. Therefore, three transistors are used for each pixel. The risetime (tr) for the liquid crystal material in display 210 is 20 ms andthe fall time (td) is 30 ms. Each transistor contains a source and adrain. The sources of each transistor are controlled by source drivercircuitry 530 a and optionally source driver 530 c. The gates of eachtransistor are controlled by gate driver 530 b. The display 210 isupdated row by row with only one horizontal row of pixels beingenergized at any given time. All of the rows are energized within avideo frame. Update formats can be interlaced or non-interlaced toproduce a frame.

[0064]FIG. 8 illustrates further circuitry 550 used by the monitor 216of the present invention. Circuitry 550 includes an LCD control board500 as described in FIG. 7. Further, circuitry 550 includes the invertercircuits 570 used to control the light sources (e.g., 132 and 136, etc.)described above in the lighting configurations. The inverter circuitry570 contains the provision for independently providing power to eachlight source (e.g., at an operating voltage of 745 volts with a strikingvoltage capability of 2,000 volts) thereby allowing independent dimmingcontrol of each light source. Each inverter circuit of 570 contains atransformer for supplying a high voltage signal to the light sources 132and 136 and also contains a switch circuit for turning the tubes off.Light sources 132 and 136 are separately coupled to power supply lines580 a-580 b. A return bus (not shown) contains a separate return linesfrom source 132 to one inverter and from source 136 to another inverter175 b. The current supplied to the inverter circuitry 570 isapproximately 2 amps at 12 volts. Logic board 575 controls whitebalancing adjustments and monitors control signals applied to display210 to ensure a proper timing interface. As described with respect toFIG. 7, the LVDS display signals over digital bus 515 originate from adigital computer system 10. Logic board 575 is also configured forreceiving a white balance adjustment control signal from digitalcomputer system 10. The data interface for controlling white-balanceadjustment will be discussed in greater detail below.

Graphics Subsystem and Electrical Interfaces for Providing GammaCorrection and White Balance Adjustment in the Flat Panel LCD Monitor ofPresent Invention

[0065] According to one embodiment of the present invention, the flatpanel LCD monitor 216 is configured for coupling to a digital computersystem to receive image data to be rendered, and to receive controlsignals such as white-balance adjustment control signals and powermanagement control signals. In addition, in the present embodiment, theflat panel LCD monitor 216 is configured for coupling to an inexpensivelight sensing device. FIG. 9 illustrates an exemplary set up of thepresent invention including computer system 10, flat panel LCD monitor216, a color-measuring device (or colorimeter) 800 a, and an inexpensivelight sensing device (or luminance sensor) 800 b. As illustrated,calorimeter 800 a is coupled to computer system 10 via serial port 17for measuring precise optical characteristics (e.g. color coordinates,color temperature) of the flat panel LCD monitor 216. In addition,luminance sensor 800 b is coupled to host computer 10 via flat panel LCDmonitor 216 and digital bus 515.

[0066] In the particular embodiment as illustrated in FIG. 9, displayoutput signals (e.g. video output signals) are compliant with the lowvoltage differential voltage signal (LVDS) format, which will bediscussed in detail below. These display output signals are suppliedover a digital bus 515 to flat panel LCD monitor 216. White balanceadjustment control signals are also supplied over digital bus 515 flatpanel LCD monitor 216. However, white balance adjustment control signalsare compliant with the inter-integrated circuit (12C) format. Asdiscussed above, flat panel backlight control circuitry 575 isresponsive to the white balance adjustment control signals to alter anet color temperature of the backlight by independently varying theintensities of light sources 132 and 136 (FIG. 5).

[0067] In the present embodiment, calorimeter 800 a is a sophisticatedtri-stimulus color sensor capable of reading precise color coordinatesand color temperature of the flat panel LCD monitor 216. Luminancesensor 800 b, on the other hand, is only capable of detecting luminancelevel, or brightness of the flat panel LCD monitor 216. Tri-stimuluscolor sensors and luminance sensors are well known in the art of colorcalibrating CRT displays. Therefore, details of the calorimeter 800 aand the luminance sensor 800 b are not described herein to avoidobscuring aspects of the present invention.

[0068] Significantly, colorimeter 800 a is configured for measuringprecise optical characteristics (e.g. luminance values, colortemperature, color coordinates) of flat panel LCD screen 210. In thepresent embodiment, optical characteristics measurement data aretransmitted to computer system 10 via serial bus 516, and are stored involatile memory 14 and data storage device 15 of computer system 10. Thestored data will then be used for profiling the flat panel LCD monitor216. The process of profiling the flat panel LCD monitor 216 using theprecise optical characteristics measurement data will be discussed indetail below. In the present embodiment, signals for controlling andinitializing light sensing device 800 are also transmitted across serialbus 516.

[0069] Luminance sensor 800 b, unlike calorimeter 800 a, is onlyconfigured for measuring luminance level, or brightness, of flat panelLCD screen 210. Luminance sensor 800 b is controlled by host computer 10via digital bus 515. In addition, luminance data measured by luminancesensor 800 b are transmitted back to the host computer 10 for storageand analysis. The luminance data will then be used for calibrating theflat panel LCD monitor 216. The process of calibrating the flat panelLCD monitor 216 using the luminance data will be discussed in detailbelow. One advantage of using the luminance sensor 800 b for calibratingthe flat panel LCD monitor 216 is that luminance sensors are relativelyinexpensive compared to calorimeters. It should be noted that, in otherembodiments of the present invention, colorimeter 800 a may be used forcalibrating flat panel display screen 210.

[0070]FIG. 10 is a block diagram of graphics subsystem 18 (FIG. 1) infurtherance of one embodiment of the present invention. As illustrated,graphics subsystem 18 comprises a graphics controller 730, a frame ratemodulator 770, a frame rate controller 780, and LVDS transmitters 710 aand 710 b. Graphics controller 730 is coupled to frame rate modulator770 by data bus 740, and is coupled to frame rate controller 780 by databus 740 and data bus 750. Frame rate controller 780 is also coupled tocontrol frame rate modulator 770. In addition, LVDS transmitters 710 aand 710 b are also coupled to receive RGB data from frame rate modulator770. In the particular embodiment as shown, graphics controller 730 isconfigured to control a flat panel backlight of flat panel monitor 216via an 12C interface.

[0071] In operation, graphics controller 730 receives image data and LUTcontrol signals from processor 12 and converts the image data toappropriate RGB values using graphics rendering engines. A color look-uptable is provided to match a specific gamma response. In the particularembodiment as illustrated, graphics controller 730 is configured forgenerating RGB values each including 10 bits (bit 0 to bit 9). Hence,bus 740 is 30-bit wide. The 2 least significant bits (LSBS) of each ofthe RGB values, however, together with horizontal synchronization (HS)and vertical synchronization (VS) signals, are transmitted to frame ratecontroller 780 to control frame rate modulator 770. The remaining 8 bitsof each of the RGB values (e.g. bit 2 to bit 9) are provided to framerate modulator 770 to be frame rate modulated. Frame rate modulation isa well known technique for generating an intermediate gray scale valueby rapidly alternating between neighboring grayscale values in CRTdisplays. As such, implementation details of the frame rate modulator770 and frame rate controller 780 are not described here in detail so asto avoid obscuring aspects of the present invention.

[0072] The frame rate modulated RGB values are provided to LVDStransmitters 710 a and 710 b via data bus 745. LVDS transmitters 710 aand 710 b then converts the frame rate modulated RGB values into LVDScompliant data format to be transmitted to flat panel LCD monitor 216.It is appreciated that, in the particular embodiment as illustrated,frame rate modulator 770 and frame rate controller 780 are implementedwithin graphics subsystem 18 of computer system 10. However, it shouldbe apparent to those ordinarily skilled in the art, upon reading thepresent disclosure, that frame rate modulator 770 and frame ratecontroller 780 may be implemented in flat panel LCD monitor 216.However, in that embodiment, transmission protocols having a very largebandwidth would be necessary for transmitting the RGB values to flatpanel LCD monitor 216. Graphics controller 730 is also configured forreceiving LUT control signals generated by gamma correction software ofthe present invention to modify the gamma of the LUT.

[0073] In addition to generating intermediate colors, frame ratemodulation technique is applied in the present embodiment to reducevisual artifacts caused by “scalloping.” The problem of “scalloping” isendemic to liquid crystal displays using nematic liquid crystalmolecules. FIG. 11A illustrates uncorrected voltage response curve 615of a typical nematic liquid crystal layer of a liquid crystal displayscreen. Also illustrated is gamma curve 625 representing an idealrelationship between relative luminance of the LCD layer and grayscaledata. As illustrated, voltage response curve 615 is not linear owing tothe threshold response nature of twisted nematic liquid crystalmaterial. Due to this non-linearity, a breakup in the smooth transitionfrom one grayscale to another will be resulted. In order to remedy thisproblem, manufacturers of LCD modules sometimes configure LCD sourcedrivers (e.g. drivers 530 a, 530 b and 530 c of FIG. 7) to generatefixed voltages in response to several specific grayscale values. Forexample, a LCD source driver, which normally generates a voltage levelof 0.04 volts in response to a grayscale value of 2, may be hardwired(or “pinned”) to generate a voltage level of 0.78 volts in response tothe grayscale value of 2. In this way, a nearly linear relationshipbetween relative luminance and grayscale would be achieved.

[0074]FIG. 11B illustrates the “scalloping” effect caused by the“pinning” particular voltages of the LCD voltage drivers. Asillustrated, curve 635 is a voltage response curve of a typical nematicliquid crystal layer of a liquid crystal display screen. Curve 635generally follows ideal relationship 625. Thus, the aforementionedproblem of unevenness in the transition of one grayscale to anotherbecomes less noticeable. However, curve 635 includes multiple “scallops”640 or unevenness, which, if uncorrected, will cause slight deviationsfrom the ideal color characteristics. These slight deviations, whilemostly unnoticeable to users of flat panel LCD monitors, are significantduring monitor calibration and profiling. These slight deviations,according to one embodiment of the present invention, may besubstantially removed by the application of the frame rate modulationtechniques. As described above, frame rate modulation techniques arewell known in the art. Therefore, it should be apparent to those havingordinary skill in the art, upon reading the present disclosure, that“scalloping” effects can be eliminated using frame rate modulator 770and frame rate controller 780 without reducing the dynamic range of theLCD monitor 216's gamma response.

[0075]FIG. 12 illustrates an exemplary LVDS implementation of thedigital video signal interface 705 between computer system 10 and flatpanel LCD monitor 216 according to one embodiment of the presentinvention. As illustrated, 24 bits of digital video data (RGB data) andup to five timing and control signals are sent from computer system 10to flat panel LCD monitor 216 through ten pairs of twisted wire 715using LVDS technology compatible with TIA/EIA-644 LVDS standards. In thepresent embodiment, the five control signals are HS (horizontal sync),VS (vertical sync), DENA (Data-Enable) used for video timing, and twogeneric control signals. Particularly, video data (RGB data) are sent tothe display through the LVDS interface at a rate oftwo-pixels-per-clock, each pixel being composed of a red, green, andblue component each being 8 bits wide. This scheme provides sufficientbandwidth for supporting a display having a screen resolution of1920×1200 at 60 Hz.

[0076] Further, as illustrated in FIG. 12, digital video interface 705includes an ODD LVDS channel comprising ODD LVDS transmitter 710 a andODD LVDS receiver 720 a. The ODD LVDS channel is dedicated for ODD RGBdata (e.g. pixel 1, pixel 3, pixel 5, etc.) and timing signals HS, VS,and DENA. Digital video interface 705 also includes an EVEN LVDS channelcomprising EVEN LVDS transmitter 710 b and EVEN LVDS receiver 720 b. TheEVEN LVDS channel is dedicated for EVEN RGB data (e.g. pixel 2, pixel 4,pixel 6, etc.) and the two generic control signals CTL1 and CTL2. It isappreciated that the digital video interface 705 illustrated in FIG. 12is exemplary only. It should be apparent to those having an ordinaryskill in the art that the digital video interface may be implementedusing other schemes as well.

[0077]FIG. 13 illustrates driver circuitry 555 of monitor 216 accordingto another embodiment of the present invention. Circuitry 555 includesan LCD control board 500 as described in FIG. 7. Further, circuitry 555includes the inverter circuits 570 used to control relative intensitiesof the light sources (e.g., 132 and 136, etc.) described above. Logicboard 590 controls white balancing adjustments and also monitors timingsignals within the LVDS video format for the purpose of powermanagement. In the particular embodiment as illustrated, logic board 590further comprises an 12C interface for coupling to luminance sensor 800b (FIG. 9). In this way, luminance data may be transmitted fromluminance sensor 800 b to computer system 10 via flat panel LCD monitor216 and digital bus 515. As described with respect to FIG. 8, logicboard 590 is Also configured for receiving a white balance adjustmentcontrol signal from computer system 10 via digital bus 515.

LCD Safe Colorimeter and Luminance Sensor for Measuring OpticalCharacteristics of the Flat Panel LCD Monitor of the Present Invention

[0078] Conventional colorimeters utilize suction cups for providing alight tight attachment to a CRT screen during color calibration.However, suction cups, when attached to an LCD display screen such asLCD screen 210, may cause a slight bowing in the glass layer resultingin a thickness differential in nematic LCD layer. This “bowing” effectis highly undesirable because the TFT layer and LCD layer of an LCDscreen may be easily damaged. Moreover, when a LCD layer is bowed, itsoptical properties are dramatically changed, causing the resultantcolors to be dramatically aberrated. Consequently, using suction-typecalorimeters on flat panel LCD monitor 216 will introduce significanterrors in the measurements of the optical characteristics during colorcalibration.

[0079] The LCD safe light sensing device 800 (e.g. calorimeter 800 a andluminance sensor 800 b) as illustrated in FIGS. 14A and 14B overcomessuch undesirable effects by avoiding the use of suction cups forattaching to the flat panel LCD screen 210. FIGS. 14A and 14B illustratea side view and a front view, respectively, of LCD safe light sensingdevice 800 according to the present embodiment. As illustrated, lightsensing device 800 includes a housing 842 for containing light sensors840, a shroud 830, and a cable 844 protruding from housing 842. Lightsensor 840 may comprise a sophisticated tri-stimulus sensor or a simpleluminance meter. Preferably, shroud 830 is made of a soft rubber foammaterial for providing a light tight environment for light sensors 840without causing significant “bowing” in the flat panel display screen210. In addition, light sensing device further includes a channel 841for coupling to non-suction type mounting means.

[0080]FIG. 14C illustrates a hanger 842 for mounting light sensingdevice 800 to flat panel LCD screen 210 according to one embodiment ofthe present invention. Hanger 842 includes J-shaped arms 815 forcoupling to a top portion of flat panel LCD monitor 216. In addition,hanger 842 further comprises a U-shaped portion 843 for securelyreceiving channel 841 of light sensing device 800.

[0081]FIG. 14D illustrates a luminance sensor 800 b mounted to flatpanel monitor 216 using hanger 842 according to the present embodiment.As illustrated, luminance sensor 800 b is rested in the U-shaped portion843 of hanger 842. In addition, J-shaped arms 815 are securely attachedto a top portion of flat panel monitor 216. In this way, shroud 830 islightly pressed against flat panel LCD screen 210 to prevent ambientlight from interfering with the monitor calibration process. FIG. 14Dalso shows an input jack 845 in flat panel LCD monitor 216 for receivingluminance data via cable 844 of light sensing device 800. Significantly,the present embodiment enables optical characteristics of the flat panelLCD screen 210 to be accurately measured. It should be appreciated thatthe light sensing device 800 and the attachment means 842 as illustratedin FIGS. 14A, 14B, 14C, and 14D are exemplary only. It should beapparent to those of ordinary skill in the art, upon reading the presentdisclosure, that many other embodiments of an LCD safe light sensingdevice which do not cause color aberration in the LCD screen may also beused.

[0082] It should also be noted that while the LCD screen 210 of thepresent embodiment contains no safeguards to prevent “bowing” caused bya suction-type attachment device, it includes features that resistcompressive forces. In the present embodiment, these features are in theform of beads or rods whose minor axes dimensions are equal to the idealliquid crystal material thickness of the cell (e.g. 4 to 5 micrometers)These “spacer” materials are positioned in between the front glass (e.g.front glass 420) and back glass (e.g. back glass 440) of the LCD screen210 before assembly. Any compressive force which tends to compress thespacing between these two glasses will be resisted by the spacer beadsor rods. Consequently, the slight pressure exerted by shroud 830 on theLCD screen 210 would not materially affect its optical characteristics.

Mechanisms for White Balance Adjustment and Gamma Correction for FlatPanel LCD Monitors

[0083] An important feature of the flat panel LCD monitor 216 of thepresent invention is that it may be color calibrated. A color calibratedflat panel LCD monitor is particularly useful for color criticalapplications such as pre-press soft proofing, desktop publishing,graphics design, medical imaging, and digital photography and videoediting, etc., which require color temperatures and gamma values ofdifferent displays to be precisely matched in order to accurate view andexchange images with confidence. In order to perform such calibrationaccurately and automatically, the present invention provides mechanismsfor white balance adjustment and gamma correction for flat panel LCDmonitors. In the present embodiments, color correction software programsstored in host computer 10, and light sensing devices are used toaccomplish the tasks of calibrating flat panel LCD monitors to a desiredset of optical characteristics.

[0084]FIG. 15 is a flow diagram 900 illustrating the processing of colorprofiling a flat panel LCD monitor according to one embodiment of thepresent invention. In the present embodiment, color profiling isperformed with an expensive tri-stimulus colorimeter such as colorimeter800 a (FIG. 9). Expensive tri-stimulus colorimeters such as calorimeter800 a are capable of precisely measuring the color coordinates ofdifferent colors displayed on the screen, and color temperatures of thescreen. Further, the expensive calorimeter used is configured formounting on a flat panel LCD screen with non-suction type attachmentmeans as described in FIGS. 14A to 14D.

[0085] With reference now to FIG. 15, at step 910, host computer 10determines whether calorimeter 800 a is properly plugged in. In thepresent embodiment, colorimeter 800 a is configured for coupling to aserial port 17 of host computer 10. Methods for determining whether aperipheral device is properly plugged into a serial port are well knownin the art, and are therefore not described herein to avoid obscuringaspects of the present invention.

[0086] At step 920, a test sequence is initiated. The initializationprocess may include completely shutting off the backlight of the flatpanel LCD monitor such that a “pure” black color (or zero luminancelevel) may be determined by the colorimeter 800 a. It should be notedthat this zero luminance level is different from the “black” luminancelevel of a LCD screen with the backlight turned on. Further, theinitialization process may include other well known self-testing stepsto ensure that the colorimeter 800 a is working properly.

[0087] At step 930, with the backlight “on,” a black luminance level ofthe LCD screen is measured by the colorimeter 800 a. Black luminancedata will then be used for calculating the contrast ratio of thedisplay.

[0088] At step 940, after the calorimeter 800 a is initialized, an imageor a series of images of known RGB values are displayed on the LCDscreen. Colorimeter 800 a is then used to measure the opticalcharacteristics, such as luminance level and color coordinates of eachRGB colors displayed on the LCD screen. The results of the measurementsare transmitted from the colorimeter back to the host computer system.As discussed above, according to one embodiment of the presentinvention, optical characteristics data of the flat panel LCD screen maybe transmitted back to the host computer system via a serial bus.

[0089] At step 950, the color temperature of the LCD screen is measuredby the colorimeter. Color temperature of the LCD screen is preferablydetermined by measuring the color temperature of “pure” white displayedon the LCD screen, i.e. all data levels of each R, G and B component setto “high.” Color temperature data are also transmitted back to the hostcomputer system via a serial bus.

[0090] At step 960, the grayscale ramps for each of the RGB primariesare determined. The grayscale ramps are determined by measuring aplurality of equally spaced grayscale points for each of the RGBprimaries at the LCD screen. For instance, the luminance levels for 32equally spaced grayscale levels may be measured and used to construct agamma curve of the LCD screen. Grayscale ramp data are then used by thehost computer to determine a gamma value of the LCD display screen usingwell known methods and algorithms.

[0091] At step 970, optical characteristics data of the LCD screen, suchas color temperature, black luminance level, gamma, color coordinates ofthe RGB primaries, are stored in the host computer in a Master colorprofile. The color profile may be used to calibrate the LCD screenperiodically such that the display's color characteristics may remainconsistent over time. In other embodiments of the present invention, thecolor profile may be transmitted across a computer network, such as theWorld Wide Web, to other computers having color calibratable displays.In those embodiments, the color profile is used as a reference such thatother monitors may be calibrated to the exact color characteristics ofthe “master” LCD screen. In other embodiments, the color profile may beused to perform screen-to-paper or screen-to-film color matching.

[0092] With reference now to FIG. 16, at step 1010, host computer 10determines whether luminance sensor 800 b is properly plugged in. In thepresent embodiment, luminance sensor 800 b is configured for coupling toan 12C interface of the flat panel LCD monitor. Methods for determiningwhether a peripheral device is properly plugged into an 12C bus are wellknown in the art, and are therefore not described herein to avoidobscuring aspects of the present invention.

[0093] At step 1020, a test sequence is initiated. The initializationprocess may include completely shutting off the backlight of the flatpanel LCD monitor such that a “pure” black color (or zero luminancelevel) may be determined by the luminance sensor 800 b. It should benoted that this zero luminance level is different from the “black”luminance level of a LCD screen with the backlight turned on. Further,the initialization process may include other well known self-testingsteps to ensure that the luminance sensor 800 b is working properly.

[0094] At step 1030, with the backlight “on,” a black luminance level ofthe LCD screen is measured by the luminance sensor 800 b. Blackluminance data will then be used for calculating the contrast ratio ofthe LCD screen.

[0095] At step 1040, after the luminance sensor 800 b is initialized, animage or a series of images of known RGB values are displayed on the LCDscreen. Luminance sensor 800 b is then used to measure the luminancelevel of each RGB primaries displayed on the LCD screen. The results ofthe measurements are transmitted to the host computer system. Asdiscussed above, according to one embodiment of the present invention,luminance data of the flat panel LCD screen may be transmitted back tothe host computer system via a digital connection, such as digital bus515, between the flat panel LCD monitor and the host computer.

[0096] At step 1050, the color temperature of the LCD screen is inferredfrom the luminance data measured by the luminance sensor. In the presentembodiment, color temperature may be inferred from luminance data andprovided that the phosphor ratios in the light sources (e.g. lightsources 132 and 136) are known. The algorithm for calculating colortemperature from luminance data of RGB primaries and known phosphorratios in the light sources are well known in the art. Therefore, theintricate algorithms for performing such estimation are not describedherein to avoid obscuring aspects of the present invention.

[0097] At step 1060, the color temperature of the LCD screen obtainedfrom step 1050 is compared to a reference color temperature value.Relative intensities of the blue and red light sources of the backlightare then adjusted according to any discrepancies between the calculatedcolor temperature and the reference color temperature value. In thepresent embodiment, the reference color temperature is contained in acolor profile stored in the host computer. The color profile may beprovided by the manufacturer of the flat panel LCD monitor.Alternatively, the color profile may be created by the profiling processdescribed above with respect to FIG. 15. For screen-to-screen matchingapplications, the color profile may be contain optical characteristicsdata of a “master” display.

[0098] At step 1070, the grayscale ramps for each of the RGB primariesare determined. The grayscale ramps are determined by measuring aplurality of equally spaced grayscale points for each of the RGBprimaries at the LCD screen. For instance, the luminance levels for 32equally spaced grayscale levels may be measured and used to construct agamma curve of the LCD screen. Grayscale ramp data are then used by thehost computer to determine a gamma value of the LCD display screen usingwell known methods and algorithms.

[0099] At step 1080, the gamma value obtained from step 1070 is thencompared with a reference gamma value contained in the color profile togenerate an appropriate transfer function. In the present embodiment,the transfer function may comprise a ratio of input digital value andoutput digital value. Further, methods and algorithms for generating theappropriate transfer function which maps one gamma curve to another arewell known in the art. Accordingly, the details of the algorithms arenot described herein to avoid obscuring aspects of the presentinvention.

[0100] At step 1090, the transfer function obtained from step 1080 isloaded into the color LUT of the graphics controller. This transferfunction accomplishes the mapping of the native transfer function of thedisplay to the reference transfer function. In this way, the flat panelLCD screen is tweaked to arrive at the desired gamma value.

[0101] A significant advantage of the present embodiment is that, asluminance sensors are much less expensive than sophisticatedtri-stimulus calorimeters, it would be economically feasible to includeone luminance sensor with every flat panel LCD monitor for performingcolor calibration. Users of color critical applications such aspre-press soft proofing and desktop publication would also find thepresent invention useful as only one expensive tri-stimulus colorimeterwould be necessary to color-match multiple flat panel LCD monitors.

[0102]FIG. 17 illustrates an exemplary graphics user interface (GUI)1100 of the white balance adjustment and gamma correction softwareaccording to one embodiment of the present invention. GUI 1100 isconfigured for displaying on LCD screen 210 of flat panel LCD monitor216. Further, as shown, the white balance adjustment and gammacorrection software is configured for running under a windows-basedoperating system, such as Microsoft's Windows NT. Particularly, the GUI1100 of the present invention comprises a window 1105 for displayinginformation.

[0103] In the particular embodiment as illustrated, GUI 1100 includes afield 1110 for displaying a currently selected color temperature, and afield 1120 for displaying a currently selected gamma value. The selectedcolor temperature and gamma value will be used in profiling process andcalibration process illustrated in FIGS. 15 and 16 respectively. Inaddition, GUI 1100 includes a field 1130 for displaying a name of thecurrently selected reference profile. As shown in FIG. 17, a “custom”profile corresponding to a color temperature of 5600K and a gamma of 1.8is selected. It should be appreciated that fields 1110, 1120, and 1130may also be used to allow users to select any possible colortemperatures and gamma values, and any predetermined and preloadedreference profiles.

[0104] GUI 1100 further includes display window 1140 for displayingimages during color calibration. As discussed above, during a colorprofiling or calibration process, an image or a series of images havingknown RGB values are displayed in display window 1140 to be measured bylight sensing device 800. According to one embodiment of the presentinvention, the display window 1140 is aligned at a center of LCD screen210 to facilitate measurement of optical characteristics by lightsensing device 800.

[0105] A system and method for providing independent white balanceadjustment and gamma correction capabilities for flat panel liquidcrystal display monitors have thus been described. While the presentinvention has been described in particular embodiments, it should beappreciated that the present invention should not be construed aslimited by such embodiments, but rather construed according to the belowclaims. The present invention has also been described in conjunctionwith a wide aspect ratio flat panel LCD monitor. However, it should beappreciated that the present invention is equally applicable to regularaspect ratio flat panel monitors running in XGA, SXGA, SVGA, UXGA, HDTV,and other display modes.

What is claimed is:
 1. A flat panel monitor for displaying informationoriginated by a host computer, said flat panel monitor comprising: agraphics controller operable to receive a gamma correction controlsignal, the graphics controller operable to adjust a gamma value of aliquid crystal display screen displaying a representation of image datain response to the gamma correction control signal, the graphicscontroller operable to adjust the gamma value without substantiallyaffecting a grayscale resolution of the liquid crystal display screen.2. The flat panel monitor of claim 1, wherein the graphics controllerincludes a color look up table to match a gamma response for the liquidcrystal display screen, the graphics controller operable to adjust thegamma response of the color look up table in response to the gammacorrection control signal.
 3. The flat panel monitor of claim 1, whereinthe graphics controller is operable to generate color values in responseto receipt of the image data and the gamma correction control signal. 4.The flat panel monitor of claim 3, further comprising: a frame ratemodulator operable to generate an intermediate grayscale value for theliquid crystal display screen in response to the color values generatedby the graphics controller.
 5. The flat panel monitor of claim 3,further comprising: a frame rate controller operable to receive asynchronization signal from the graphics controller, the frame ratecontroller operable to control modulation performed by the frame ratemodulator in response to the synchronization signal.
 6. The flat panelmonitor of claim 5, wherein the synchronization signal includeshorizontal synchronization and vertical synchronization values.
 7. Theflat panel monitor of claim 1, further comprising: a controller circuitoperable to receive a white balance adjustment control signal, thecontroller circuit operable to adjust a white balance of the liquidcrystal display screen in response to the white balance control signal.8. The flat panel monitor of claim 7, wherein the controller circuitadjusts the white balance of the liquid crystal display screen withoutsubstantially affecting a grayscale resolution of the liquid crystaldisplay screen.
 9. The flat panel monitor of claim 1, wherein thegraphics controller is operable to provide a backlight control signal tocontrol a backlight of the flat panel monitor.
 10. The flat panelmonitor of claim 1, wherein the gamma correction control signal isgenerated in response to a comparison of optical characteristics of theliquid crystal display screen and reference optical characteristics. 11.A method for displaying information on a flat panel monitor, comprising:receiving a gamma correction control signal; adjusting a gamma value fora liquid crystal display screen in response to the gamma correctioncontrol signal, the gamma value being adjusted without substantiallyaffecting a grayscale resolution of the liquid crystal display screen12. The method of claim 11, further comprising: comparing opticalcharacteristics of the liquid crystal display screen to referenceoptical characteristics; generating the gamma correction control signalin response to the comparison.
 13. The method of claim 11, furthercomprising: generating color values in response to receipt of image dataand the gamma correction control signal.
 14. The method of claim 13,further comprising: generating an intermediate grayscale value for theliquid crystal display screen in response to the color values.
 15. Themethod of claim 11, further comprising: adjusting a white balance of theliquid crystal display screen without substantially affecting agrayscale resolution of the liquid crystal display screen.
 16. A methodfor providing image data to a flat panel monitor, comprising: generatingan uncorrected color value in response to receipt of image data;translating an uncorrected color value to a corrected color valueaccording to an actual gamma response for a liquid crystal displayscreen; displaying the image data with the corrected color value withoutsubstantially affecting a grayscale resolution of the liquid crystaldisplay screen.
 17. The method of claim 16, further comprising:determining grayscale ramps for the liquid crystal display screen;determining the actual gamma response for the liquid crystal displayscreen from the grayscale ramps.
 18. The method of claim 16, furthercomprising: comparing the gamma response for the liquid crystal displayscreen to a reference gamma response; generating a transfer function tomap the reference gamma response to the actual gamma response.
 19. Themethod of claim 16, further comprising: maintaining the gamma responsefor the liquid crystal display screen in a look up table.
 20. The methodof claim 16, further comprising: modulating the corrected color value toproduce an intermediate grayscale value.